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Results are presented from a search for periodic variations in the brightness and color indices of the active star PZ Mon based on many years of photometric data from 1992 to 2015. The photometric period derived from the entire set of observations is 34.16 days, but the period may vary by 1.5% within individual intervals. The color index V-R varies with the same period. These variations are indicative of reddening of the star with decreasing brightness. A correlation between the values exists over the entire observation interval. The variations in B-V occur over an interval of 26-28 days. A nonuniqueness in these variations shows up in a brightness-color index diagram: a reduction in the color index with decreasing brightness is observed in some epochs, which can be explained in terms of a spottedness model by the presence of cold, as well as hot, formations on the star’s surface.

The star Θ1 Ori C1, which is the nearest companion of the principal star Θ1 Ori C, is studied using extensive spectral data. Two radial velocity curves are constructed and solved. One of these describes the motion of the principal star and the other, the motion of the companion C1; in both cases the stars rotate about the center of mass of the C + C1 system. The physical parameters (temperature, acceleration of gravity, mass) and chemical composition of the star C1 are determined. A periodicity of 15.4 days associated with the rotation of the principal star is identified in the variations of the radial velocity.

The results of spectrophotometric observations of CH Cyg in an active phase and during emergence from it are given: the spectral energy distribution in the 3225-7500 A range with 23 A resolution, the absolute monochromatic illuminances at eight selected wavelengths in the 3225-8015 A, and the emission fluxes in the Hα and Hβ lines. The features of the energy distribution in the stellar spectrum and the observed forms of variability, different between the short-wavelength and red parts of the spectrum, are determined by the instability of both of the system's components. In the active phase, CH Cyg's emission in the observed spectral range can be represented as the total emission from a cool M6 III giant and a hot hydrogen gas with a temperature T e = 10,000-15,000 K. In the low-brightness state, the star's energy distribution fully corresponds to that of a cool giant, the spectrum of which varies from M6 III to M7 III. The photometric variability of the cool component in the λ 8015 A range is 0 m .3-0 m .4. An increase in the brightness of the cool giant preceded a bright outburst of the hot component.